A silver sulfide sol was prepared by mixing equal concentrations of a silver sol with a sulfur sol. The mixture was stirred for 30 minutes until there was no further change in color. The sulfur sol was prepared by dissolving solid sulfur in hydrazene followed by addition of distilled water. The mixture was heated at 75 deg C for 30 minutes to allow the sol to develop. The silver sol was prepared by reduction of silver nitrate with a mixture of 10% dextrin and 10% sodium hydroxide. The mixture was stirred for 30 minutes.